WETTING TRANSITION OF A BINARY-LIQUID DUE TO SUPPRESSION OF ELECTROSTATIC FORCES

When a phase-separated mixture of carbon disulfide and nitromethane is put in contact with borosilicate glass, a thick nitromethane-rich wet ting layer generally results. The long-range force responsible for thi s layer is believed to be electrostatic in nature and caused by ioniza tion of hydroxyl groups on the glass surface. We have used a capillary -rise experiment to examine the effect on the state of wetting of supp ressing this force through the addition of a soluble salt, tetrabutyla mmonium iodide. We find that for small salt concentrations (< 0.1M) th e glass appears to remain completely wet to within at least 40 K of T( c), but that for larger concentrations (> 0.2M) the glass is incomplet ely wet for temperatures T < (T(c) - 25 K). At T almost-equal-to (T(c) - 25 K) the system undergoes a wetting transition from incomplete to complete wetting. The appearance of this wetting transition seems to r esult from the complete removal of the long-range electrostatic intera ction.